I'm done...

[Lloyd Smale]

When I built my 300 BO (Carbine length) I needed an adjustable gas valve on the barrel to get reliable functioning at subsonic speeds with light bullets. Have you considered changing your gas block and cranking it down almost all the way so you can back off on velocity? Lead deposits anywhere in the system are not desirable nor do they add to accuracy nor functionality.

I’m pretty much of a novice with the Blackout guns, but that’s how I would attack your problem (before investing in a new barrel with only slightly slower twist!)

Froggie

I think you've got it backwards. For those light loads and subsonic loads you want all the gas you can get so a standard wide open gas block (non adjustable) is perfect. Its when you start cranking up the pressures that an adjustable gas block can be a benefit. It lets you back off the gas and use only what you need.

[GooseGestapo]

Two pages and nobody mentions the most important consideration.
What is your sizing diameter?...

My .300BO shoots under 2moa with any cast bullet I’ve run through it. Running 1850-1,900fps.
I’m mostly using the Lee 155gr SemiPoint GC of w/w with 2%An/Sb solder added and lubed with SPG and Hornady GC’s. Also feeds Lee 150gr FNGC.
Also HF pc’d.

But I’m sizing .311”!
If you are sizing.308” or .309”, THERE is your problem.
My barrel is a No name 16” Mid length gas port, 1/8” twist. so will only cycle with supersonic ammo. I use Rl7, 4198, H110 and 1680 with equal success.

[Burnt Fingers]

I'm sizing to .310

I might have to give .311 a try. I think I have a NOE bushing in that size.

[Burnt Fingers]

Try the 350 Legend instead. Easy conversion.

I've been eyeing the 350 Legend pretty hard.

I haven't seen much about how it does in a shorter barrel though.

[cwlongshot]

Pryor to this year, I had the same story.
My Blk out shooting the loads they liked where better then I could have ever expected or hopped they might be. Im speaking UNDER 1/2 MOA. HONEST 1/3&1/4 MOA shooting!!



But cast was a frustration. I tried everything I had. I bought a couple molds BOUGHT bullets from couple suppliers. Took bullets from
Guys on
On line & friends who had success. Nope nothing shot to my satisfaction. Maybe my hopes are too high but I want sub 2" @ 100 and sub 1" @ 50. Sometimes Ill get there then a flyer will ruin things.

This year, I assembled another MSR in 300 and focused on sub loads. I bought a couple and loaded a BUNCH! I picked up Lyman Londs 311299, 311335, 311284 HP & Ideal 308389. Along with Lees 312-1552r and 160TL molds.

I sized 309,310 & 311 for all. I shot them GCd and not. I shot them subs and supers. I shot them conventional lube, TL and mostly PC.

A friend wanted some of my NOE 178RD bullets for his 30/30. I cast them with the deep HP pin for a 165g bullet. PC in Clear. I had them on hand and had 3032 in the hopper for the 30/30.... I loaded up 10 with 15.3g 3031 and that 165 HP seated @ crimp groove. This load cycled but refused to feed... BUT IT PUT BULLET AFTER BULLET INTO ONE HOLE @ 50 yards!!! Im talking a 50cal sized hole for all ten shots!!!!

Since then 4227 & RE7 have both done ALMOST as good. BUT ONLY WITH BULLETS THAT DONT FEED!! ?!?!?!??? GRRRR

I GOT THE LEE molds next. With high hopes I loaded both with 3031 & RE7. 16g was toos for the 155 shooting a loose 1" group in FOUR 300's the first day. The 160 was 1.5-2". Next week same rifles and ammo produced nearly same results but I moved to 100yards. 1.5 ish was bestnoutta the 155 @ 1300 fps. The 160 was 4" plus. (I really need to swear off TL bullets. They never shoot for me)

The 311299 (210g) shot pretty wall with all 4227 loads and OK with RE7.

The 311335 (220g) is still under the micro scope

The 311284 is a HP (208g )and needs to be tested. I just cast some last week and need time to season before testing.

Havent tested the 308389 yet. Its a very pointy 190g

Overall, I think that LEE 312-155 is my best and maybe can be refined more. I can hit steel out past 200 all day but thats a 12" plate... Not exactly precision.

My advice. Try more bullets!!

PM me and for postage Ill send ya what I have to try. Then you can buy your own mold if they pan out!

CW

[Dusty Bannister]

Is the fail to feed due to nose length preventing full chambering, or due to a fat nose not allowing the cartridge to enter the lands?

[Larry Gibson]

What was the velocity of the loads?

There is an RPM threshold of 120-140,000 RPM with cast bullets, especially the longer ones spun in fast twist. You're in that range at 1300 fps. Around 1350 - 1360 fps is going to be 140,000 +/- RPM given the 7" twist of your barrel. I suggest using a GC'd heavier bullet and drop the velocity to 1000 - 1300 fps.

[ACC]

I've been trying to get cast boolits to shoot in my 300 Blackout AR Pistol for a few months now.

Nothing seems to work. I really wanted the MP 311410 boolit to work. If I can keep five rounds on a paper plate at 20 yards it's a miracle.

The NOE 311-158 FN is SLIGHTY better.

NOE 311-198 SP doesn't group either.

MP 311-235 is my last hope.

With the other four bullets, HP and solid on the 311410, I've tried a total of 72 loads. Several different powders.

The barrel is a 8.5" 1:7 twist. It will shoot j-word 125 gr bullets and 147 gr bullets into small holes.

Cast....forget about it.

It it too much to ask to have a semi-accurate cast load that functions in an AR-15?

Back off the powder charge. Some times some guns will not shoot cast boolits except if they are slow. Like around 1200 FPS. These will not work the action though.

ACC

[Burnt Fingers]

What was the velocity of the loads?

There is an RPM threshold of 120-140,000 RPM with cast bullets, especially the longer ones spun in fast twist. You're in that range at 1300 fps. Around 1350 - 1360 fps is going to be 140,000 +/- RPM given the 7" twist of your barrel. I suggest using a GC'd heavier bullet and drop the velocity to 1000 - 1300 fps.

Hmm....

I was really hoping to shoot lighter weight cast boolits in this firearm. It sounds like the only way to accomplish that is going to be a custom barrel.

[Larry Gibson]

Hmm....

I was really hoping to shoot lighter weight cast boolits in this firearm. It sounds like the only way to accomplish that is going to be a custom barrel.

That does seem to be your conundrum.....

Your barrel was intended for heavy for caliber bullets at sub-sonic velocity. The fast twist is needed to stabilize those. If you want to shoot lighter weight cast bullets without any regard for them being sub-sonic then a barrel with a slower twist would be a good idea. A 14 or 16" twist will do for 150 gr bullets or less. The 30 Carbine's use a 18 or 20" twist. A 12" twist would be the fastest I would suggest and really may be best for bullet weights of 125 - 200 +/- gr weight for sub-sonic to 2000 fps +/- depending on bullet weight and length of barrel. That is with the 30 BO cartridge.

[Burnt Fingers]

That does seem to be your conundrum.....

Your barrel was intended for heavy for caliber bullets at sub-sonic velocity. The fast twist is needed to stabilize those. If you want to shoot lighter weight cast bullets without any regard for them being sub-sonic then a barrel with a slower twist would be a good idea. A 14 or 16" twist will do for 150 gr bullets or less. The 30 Carbine's use a 18 or 20" twist. A 12" twist would be the fastest I would suggest and really may be best for bullet weights of 125 - 200 +/- gr weight for sub-sonic to 2000 fps +/- depending on bullet weight and length of barrel. That is with the 30 BO cartridge.

I played around with the numbers last night and a 1:12" would be the fastest. Now to find a custom barrel that doesn't cost more than I have in this build.

[upnorthwis]

My 8:1 twist 5.56, With gas check = 2" or less @ 100 yds. Without gas check = Minute of berm or larger. There are people that say they get good results with PB, but I haven't seen it.

[lilMAC25]

I’m shooting the 247 gr NOE PB (subsonic) and not having any issues.

[Lloyd Smale]

I size to 309. Why because any bigger and they wont chamber in and of my 3 ar15s reliably and anything bigger then 310 wont even chamber in my ruger American. Even at 309 I about cant crimp because they then wont chamber so I just straighten out the flare in the crimp die. My 16 inch ar and American will do less the 2 moa at a 100 yards with 309s with the second load I tried (same load in both guns) So I guess I ask myself what 2moa wont take care of. It will easily give killing hits on man or deer sized targets at 300 yards. So as long as im not competitive shooting which I don't I have no need to find some magic 3/4 inch group load. Matter of fact I had a ball the other day. Just for grins I loaded some of the 130 rcbs spitzers with 4.5 grains of unique for a sub sonic load for my American with a can on it. They shocked me. I was expecting MAYBE 2 inch 50 yard groups and they ended up shooting 2 inch at a 100 yards! Sized? 309. A properly cut 30 cal barrel doesn't need bullets bigger then 309. They seem to do pretty good with jacketed at even 308.

Two pages and nobody mentions the most important consideration.
What is your sizing diameter?...

My .300BO shoots under 2moa with any cast bullet I’ve run through it. Running 1850-1,900fps.
I’m mostly using the Lee 155gr SemiPoint GC of w/w with 2%An/Sb solder added and lubed with SPG and Hornady GC’s. Also feeds Lee 150gr FNGC.
Also HF pc’d.

But I’m sizing .311”!
If you are sizing.308” or .309”, THERE is your problem.
My barrel is a No name 16” Mid length gas port, 1/8” twist. so will only cycle with supersonic ammo. I use Rl7, 4198, H110 and 1680 with equal success.

[Burnt Fingers]

After Saturday's range trip I've come to the conclusion that this barrel doesn't like cast bullets.

30 different heavy bullet loads and none of them would group.

[Conditor22]

http://www.x-caliber.net/custom-ar-barrel for $300

[tomme boy]

Who made the barrel?

Also the throat is the problem. They are throated long for the 200+gr bullets. They are not entering the bore straight.

[Conditor22]

I got a AR 300 BO Davidson Defense "Mercs" AR-15 Upper Receiver 16" .300 Blackout 4150 CMV 1-8T Barrel 15" M-Lok Handguard
@ 50 yards, initial load development, still need to fine-tune

rifle (had to seat the boolit 1/8" deeper to go into battery )
H110 8.1grn 7/8 group 247 FN GC
h110/296 8.7grn 1/2 group 1045fps L 312-155-2R

pistol

300 AAC BO 700X 4 1" NOE 247 FN GC

haven't tried the 155 grn

[Burnt Fingers]

Who made the barrel?

Also the throat is the problem. They are throated long for the 200+gr bullets. They are not entering the bore straight.

I'm not sure who made the barrel. If it's a throat problem then nothing I do can change that.

But here's the rub. I shot long boolits out of if this weekend. Same problem as lighter weight cast boolits. If the MP 235 isn't long enough then nothing is.

[Conditor22]

OK thinking outside the box, does the crown look OK?